Furnace for brazing



Sept. 28, 1937.

E. B. WELCH FURNACE 'FoR BRAZING Filed June 22, 1936 4 Sheets-Shet l INVENTOR Spt. 28, 1937. w c 2,094,249

FURNACE FOR BRAZING Filed June 22, 1. 56 4 Sheets-Sheet 2 49 INVENTOR Sept. 28, 1937. E. B. WELCH FURNACE FOR BRAZING Filed June 22, 1936 4 Sheets-Sheet 3 mwm 0M? INVENTOR E. B. WELCH Sept. 28, 1937.

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Patented Sept. 28, 1937 UNITED STATES PATENT OFFICE FURNACE FOR BRAZING Elmer B. Welch, McKe esport, Pa., assignor to Application June 22, 1936, Serial No. 86,443

Claims.

This invention relates to brazing furnaces adapted for brazing tool tips to tool shanks. These tool tips are generally made of a hard cemented composition such as tungsten carbide 5 bonded by cobalt.

In the accompanying drawings which illustrate a preferred embodiment of my invention,

Figure 1 is a side elevation of a brazing furnace with the side guard which protects the electrical connections removed;

Figure 2 is a front elevation of the furnace with a part of one of the side guards removed to show the electrical connections;

Figure 3 is a longitudinal vertical section through the furnace taken on the line III-III of Figure 2;

Figure 4 is a perspective view of one of the molded heat insulating blocks employed in the furnace for forming the heating chamber and insulating the muffle;

Figure 5 is a perspective view of one of the muffles, two of such muffles being employed in the embodiment of the furnace shown;

Figure 6 is a perspective view of the front collar which fits over a portion of the mufile shown in Figure 5;

Figure '7 is a perspective view of the rear collar which also fits over a portion of the muiile shown in Figure 5;

Figure 8 is a front elevation of a cap employed for closing the rear end of the mufile;

Figure 9 is a vertical section taken on the line IXIX of Figure 8 showing the cap and also showing the connections extending through the cap for introducing a non-oxidizing gas into the muflie;

Figure 10 is a perspective view of a plate on which certain electrical connections are mounted, the plate also supporting a side guard shown in Figure 11; and

Figure 11 is a perspective view of a side guard employed for protecting the electrical connections of the furnace.

The furnaces now commonly employed for brazing tool tips to tool shanks are relatively long, say, about 8 feet in length. They are of the muffle type containing a refractory muffle such as aluminum oxide wound on the outside with heat resisting wire such as molybdenum wire, through which an electric current is passed in order to heat the muffle. The space outside of the muffle and inside of the casing is filled with an insulating material. Hydrogen or other non-oxidizing gas is fed through the muille chamber so as to prevent oxidation of the assembled parts during brazing. A flux such as borax is generally employed in the brazing operation, which flux would attack the refractory muflle if not protected. Accordingly, it is customary to place the assembled tool shank and tip in a car bon boat and to heat the parts to brazing temperature while contained in the boat so as to prevent spilling of the flux onto the refractory muffle. These boats are about 8 inches long, 3 inches wide and inch in depth so that they provide considerable mass which absorbs a large quantity of heat. These boats containing the assembled parts are pushed into the furnace and after the brazing has been accomplished, are pushed out at the other end, after which they cool so that each time it is necessary in carrying out a brazing operation to heat these boats up to temperature.

The refractory muffle is wound throughout substantially its whole length with resistance wire H so that substantially the whole length of the muffle chamber is heated to a high temperature. The boats containing the assembled parts are pushed through this long muffle, but it is difficult to observe the conditions of the tool tip, solder and flux due to the fact that when the assembly is pushed into the furnace, it is some distance away from the operator. Hydrogen has to be supplied to the mufile chamber not only during the brazing operation, but also while the muflle chamber is being brought up to and cooled down from brazing temperature. This is necessary in order to prevent the molybdenum heating wire from oxidation. It generally takes from 5 to 6 hours to heat the furnace up to brazing temperature because of the large amount of heat insulating material employed in the furnace. Time is of considerable importance in this brazing method because the tool tips are brazed to the. shanks on each order and may not be made up ahead of time and stocked. It is therefore advantageous to provide some method whereby the furnace may be rapidly heated up and the brazing operation may be rapidly conducted. In the old type furnace, hydrogen had to be passed through the muffle for a suflicient time to expel all air before the electric current was turned on because otherwise there was danger of the mixture of air and hydrogen exploding.

These disadvantages of the old type furnace have been eliminated or decreased by the present invention, in which a relatively short furnace is employed. The muflle instead of being made of porous refractory non-metallic material such as aluminum oxide or silicon carbide, is made of a heat-resisting metal alloy. The heat which is applied to the muffle chamber is limited to only a small portion of the length of the mufile chamher so as to localize the heat about the tool tip and the portion of the tool shank immediately adjacent the tool tip. This is preferably accomplished by providing a heating chamber which surrounds a portion of the muffle intermediate the ends of the rnuflie, the heating chamber extending for only a short distance along the mufiie. The heating chamber in the embodiment shown is only approximately 3 inches in length. It is provided with non-metallic electric resistance heating elements such as silicon carbide rods; The muiile is short, being about 9 inches long in the embodiment shown. This enables an operator to look into the furnace and clearly observe the condition of the assembly. In my furnace it is unnecessary to tie the tool tipto the toolshank with wire, as was the case in the old type furnace. If the tip gets slightly out of place, it may be withdrawn from the muffle by a pair of tongs, the tip pressed into correct position by the application of slight pressure, and the assembly immediately returned to the interior of the muffle and the brazing continued. This was notpossible in the old type furnace because of the length of the muliie. Also, because the operator could not look into the mufiie for a sufiicient distance to see if the tip was in its proper place.

Referring more particularly to the accompanying drawings, the furnace comprises two muflies 2 extending throughout the length of the furnace. These muffles are made of a heat-resisting alloy which is impervious to gases. One such alloy contains about Percent Chromium 28 Nickel 1 Carbon .25 Manganese 1 Iron Balance Each muffle is generally cylindrical in shape with a flat bottom it. The front end 4 is open, but the rear end is closed by a cap 5 illustrated in Figures 3, 8 and 9. The cap. corresponds generally in shape to the muffle and is provided with an outer flange 6 and an inner flange 1 forming a channel 8 between them. The end of the mufile fits into the channel and the joint is sealed by heat-insulating packing material 9. The cap is secured to the muffle by screws It. Hydrogen or other non-oxidizing gas is introduced into the interior of the muflle through a pipe l2 which is threaded into an opening provided in a boss I3 on the cap. A smaller pipe i4 is threaded into a boss l5 on the inside of the cap, and the inner end l6 of the pipe is bent downwardly so as to direct the hydrogen against the bottom of the muffle.

The muffles are heated by non-metallic electric resistance heating rods H such as silicon carbide rods located in a heating chamber l8, one heating element being located'above and the other below the muliles. The heating chamber l8 extends along the muffle for only a small portion of its length, thereby providing a heating zone which is of limited extent. The heating chamber extends transversely of the muffles and is considerably longer in a direction transverse of the muflies than longitudinally of the muiiles.

A refractory non-metallic collar 2@ fits over the front portion of each of the muiiles 2, and

a similar but longer collar 2! fits over the reai portion of each mufiie. The space between the collars and the sheet metal casing 22 which extends around the top and sides of the furnace is occupied by two complementary, molded heatinsulating blocks 23, as illustrated in Figure 4. These two insulating blocks are similar to each other, one being used above the muffles and the other below them. Each block is provided with two slots 25 extending from the front to the rear of the furnace and adapted to receive the muffles 2. Each of the blocks also is provided with a slot 26 having a curved bottom 2ll, the slot 26 extending transversely to the slot 25. When the two blocks are fitted together, one above and one below the mufiles, the slots 26 form the heating chamber 18 which receives the electric resistance heating rods ll. Openings 28 extend through the ends of the blocks for receiving electrical contact posts in which the resistance rods ii are mounted, as will be described later. Front and rear'plates 2S and 23% connected by tie rods 3! are used to secure the various parts of the furnace in assembled position.

The electrical connections for the heating rods are shown in Figures 1 and 2. Similar connections are provided at each end of each of the heating elements so that it will be necessary to describe only one of these sets of connections. The right-hand end of the upper heating element ii, as viewed in Figure 2, fits into a socket 33 in a contact post 3 3. The other end of the contact post is rounded and fits into a socket formed in a contact plate 35. The contact plate is riveted as indicated by the reference numeral 36 to a contact spring 3? shown most clearly in Figure 1. The contact spring 3? is mounted on an insulating block 38 by means of a threaded binding post 3%? secured to the block. The post 39 extends through a slot (not shown) in the contact spring 3!. Awing nut 36 is threaded on the post 39 so that by tightening the wing nut, the tension of the spring 3i on the contact post 3 5 may be adjusted. The contact spring 3? also is provided with a slot 4! which receives a guide pin 62 secured to the insulating block 38. The two slots in the contact spring 31, and the guide pin 452 permit guided adjustment of the contact spring relative to the post 39. A wire 43 connects the binding post 39 to a binding post M provided with a wing nut $5, the binding'post lt being mounted an insulating block it.

The electric current which is supplied through the conductor 31 flows through the wire 43 to the binding post 38 to the contact spring 3'1, and then through the contact post to the resistance rod if. By means of similar connections on the left-hand end of the rod ll, as viewed in Figure 2, the current flows through a conductor 48 to the lower heating rod if, then through the connections at the right-hand end of the lower rod, then through a wire 43a to the binding post 54a which is connected to the wire l'i'c. The electrical connections for the resistance rods l'i are protected by guards 59, one of which is shown in Figure 11. These guards are of sheet metal and are open at the top and bottom. They are secured to the furnace so that they may be quickly removed in order to adjust the electrical connectionsor replace a resistance rod. Each guard is secured by screws 59 to posts 5B carried by a plate 52 which is secured to the side of the furnace. Each plate is provided with two openings 53 through which the contact posts 3d extend.

A pyrometer 54 extends into the furnace through the rear plate 30 and is connected to an indicator 55 mounted on a bracket 56 secured to the plate.

A tool tip and shank are shown in brazing position in the furnace in Figure 3. The tool tip 51 fits in a recess 58 provided in the shank 59. It will be noted that the heating chamber I8 extends for only a small portion of the length of the muffle, so that the heat is localized and limited to the tool tip and only a small portion of the tool shank adjacent the tip. This leads to very accurate control of the temperature within the heating zone of the mufile chamber and conserves considerable heat since the main portion of the tool shank is not heated to a high temperature. The heating chamber preferably extends along the muffle for a distance not over three times the length of the tool tip.

In carrying out a brazing operation, flux such as borax is placed in the recess 58 of the tool shank when the shank is resting on the ledge 60 at the front of the furnace. The shank is then inserted into the heating zone and heated until the flux flows freely. It is withdrawn from the furnace by the operator grasping the shank with a pair of short tongs and the tip is put in place. A small piece of copper about .003 inch thick bent double is placed over the joint between the tip and the shank and the assembled parts are then introduced again into the heat zone. The temperature within the muffle is maintained at about 2050 F. After the copper is melted, the shank and tip are moved toward the front of the furnace, a portion of the shank extending out from the furnace, but the tip and shank portion adjacent to it remaining just within the muffle so as to be protected by the hydrogen gas within the muffle. While in this position, light pressure is applied to the tip with a hand tool to seat it firmly in place. This is done while the copper is still in molten condition and can be accomplished because of the shortness of the furnace and the ease and quickness with which the assembly can be withdrawn. When the tip and solder have cooled sufficiently, the tool is withdrawn from the furnace.

After a muflle has been in use for some time, it may become distorted or warped along that portion which lies within or adjacent the heating chamber. In my furnace, the muffle can be easily withdrawn from the furnace and straightened or a new muffle substituted. This is easily done by removing one or both of the refractory collars 20 or 2| before or at the same time as the muffle is being withdrawn from the furnace. By removing the collars, suflicient space is provided between the muffle and the molded refractory heat-insulating blocks 23 to enable the muffle to be withdrawn even though it has warped considerably. In the old type furnace it was necessary to tear out a large part of the insulation and practically re-insulate when it was necessary to replace a muflle with a new one.

It will be noted from Figure 3 that the heating chamber l8 does not lie at the middle of the muffles 2. It is displaced somewhat from the middle of the muflles toward the front ends thereof. By this arrangement the useful life of the muflles is doubled. It is necessary that the bottom of a muffle be flat in order toproperly support the tool tip and shank during the brazing operation. After a muffle has been in use for some time it becomes warped at that portion within the heating chamber, so that the bottom of the muffle will not properly support the tool tip and shank. The refractory collars 20 and 2| are then removed and the muffle withdrawn from the furnace. The muffle is withdrawn, reversed end for end and again inserted in the furnace within the collars. This reversal presents a new, non-warped, flat bottom muffle portion to the heating chamber for properly supporting the tool tip and shank. Before reversing the muffle, it may be ground slightly to remove the warped portion, but this is usually not necessary.

Although it is preferred to provide the heat for the furnace by means of electric resistance elements, preferably non-metallic electric resistance elements, other types of electric resistance heating elements may be employed, or gas, oil orother fuel may be utilized in the heating chamber by providing a suitable outlet for the products of combustion.

I have illustrated and described the present preferred embodiment of my invention. It is to be understood, however, that the invention may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. A furnace for brazing tool tips to tool shanks, comprising a heat-resisting metallic muffle, a heating chamber outside the muffle and extending for only a small portion of the length of the muffle to as to localize the heat in the muffle, heat insulating material around the muffle and heating chamber, and a removable collar between the muffle and heat insulating material adjacent each end of the muffle, said removable collars contacting with and supporting the muffle along the major part of those portions of the muffle which extend between the heating chamber and the ends of the muffle.

2. A furnace for brazing tool tips to tool shanks, comprising a heat-resisting metallic muffle having a flat bottom and being open at one end and closed at the other, a heating chamber outside the muffle and extending for only a small portion of the length of the muffle so as to localize the heat in the mufile, heat insulating material around the muffle and heating chamber, the portion of the interior of the muffle adjacent the heating chamber being unobstructed, and means for supplying a protective gas to the interior of the muffle.

3. A furnace for brazing tool tips to tool shanks, comprising a heat-resisting metallic muffle having a flat bottom and being open at one end and closed at the other, a heating chamber outside the muffle and extending for only a small portion of the length of the muffle so as to localize the heat in the muffle, non-metallic electric resistance heating elements in the heating chamber, heat insulating material around the muffle and heating chamber, the portion of the interior of the muffle adjacent the heating chamber being unobstructed, a removable collar between the muffle and heat insulating material adjacent each end of the muffle, each of said removable collars extending inwardly of the furnace to a point closely adjacent the heating chamber and supporting the muffle, and means for supplying a protective gas to the interior of the muffle.

4. A furnace for brazing tool tips to tool shanks, comprising a heat-resisting metallic muffle having a flat bottom and being open at one end and closed at the other, a heating chamber outside the muffle and extending for only a small portion of the length of the muffle so as to localize the heat in the muffle, non-metallic electric resistance heating elements in the heating chamber, heat insulating material around the mufile and heating chamber, the portion of the interior of the mufile adjacent the heating chamber being unobstructed, a non-metallic removable collar between the mufile and heat insulating material adjacent each end of the muiile, each of said removable collars extending inwardly of the furnace to a point closely adjacent the heating chamber and supporting the muffle, a cap closing an end of the muffle, the cap having a channel for receiving the end of the mufile, sealing means in the channel means for securing the cap to the muflle, and means for conducting a protective gas into the mufile through the cap.

5. A furnace for brazing tool tips to tool shanks, comprising a heat-resisting metallic mufile having a flat bottom and being open at one end and closed at the other, a heating chamber outside the muflie and extending for only a small portion of the length of the muffle so as to localize the heat in the muffle, the portion of the interior of the muflle adjacent the heating chamber being unobstructed, heat insulating material around the mufile and heating chamber, a removable collar between the muffle and heat insulating material adjacent each end of the mufile, each of said removable collars extending inwardly of the furnace to a point closely adjacent the heating chamber and supporting the mufile, and means for supplying a protective gas to the interior of the muffle.

ELMER B. WELCI-I. 

